Memory-dependent adjustment of vocal response latencies in a territorial songbird.

Vocal interactions in songbirds can be used as a model system to investigate the interplay of intrinsic singing programmes (e.g. influences from vocal memories) and external variables (e.g. social factors). When characterizing vocal interactions between territorial rivals two aspects are important: (1) the timing of songs in relation to the conspecific's singing and (2) the use of a song pattern that matches the rival's song. Responses in both domains can be used to address a territorial rival. This study is the first to investigate the relation of the timing of vocal responses to (1) the vocal memory of a responding subject and (2) the selection of the song pattern that the subject uses as a response. To this end, we conducted interactive playback experiments with adult nightingales (Luscinia megarhynchos) that had been hand-reared and tutored in the laboratory. We analysed the subjects' vocal response latencies towards broadcast playback stimuli that they either had in their own vocal repertoire (songs shared with playback) or that they had not heard before (unknown songs). Likewise, we compared vocal response latencies between responses that matched the stimulus song and those that did not. Our findings showed that the latency of singing in response to the playback was shorter for shared versus unknown song stimuli when subjects overlapped the playback stimuli with their own song. Moreover birds tended to overlap faster when vocally matching the stimulus song rather than when replying with a non-matching song type. We conclude that memory of song patterns influenced response latencies and discuss possible mechanisms.

Do Barbary macaques 'comment' on what they see? A first report on vocalizations accompanying interactions of third parties.

Primates acquire knowledge about relationships of third parties and group structure by monitoring their conspecifics. We show that Barbary macaques (Macaca sylvanus) utter specific vocalizations while monitoring interactions of other group members. As they did not direct other behaviours to the interacting group members, we provisionally termed these vocalizations 'vocal comments'. We investigated the acoustic properties of these comments and the social contexts in which they occurred. Most adult males and females of two studied groups produced low-amplitude calls when observing close contact interactions of other group members. The acoustic features of these calls varied with characteristics of the commented situation. Our results suggest that such calls might not be directed towards the agents of the commented situation, but towards other group members. The vocal comments may signal the caller's awareness of the observed interaction and possibly attract the attention of others to the situation.

From birdsong to speech: a plea for comparative approaches.

Human language and speech are unique accomplishments. Nevertheless, they share a number of characteristics with other systems of communication, and investigators have thus compared them to birdsong and the vocal signaling of nonhuman primates. Particular interesting parallels concern the development of singing and speaking. These behaviors rely on auditory perception, subsequent memorization and finally, the generation of vocal imitations. Several mechanisms help young individuals to deal with the various challenges during the time of signal development. Specific differences aside, astounding parallels can be found also in how a human and a particularly accomplished bird like the Common Nightingale Luscinia megarhynchos treat the experience of many different sound patterns or songs. As a consequence of such exposure, both human infants and young birds eventually acquire large repertoires of verbal or vocal signals. These achievements, however, require access to specific memory mechanisms which are well adapted to the purposes they serve, thereby allowing them to fulfil their species typical roles. With such aspects as a reference, birdsong is an excellent biological model for memory research and also an appropriate system for the study of evolutionary strategies in a very successful class of organisms.

Approaches to the mechanisms of song memorization and singing provide evidence for a procedural memory.

There is growing evidence that, during song learning, birds do not only acquire 'what to sing' (the inventory of behavior), but also 'how to sing' (the singing program), including order-features of song sequencing. Common Nightingales Luscinia megarhynchos acquire such serial information by segmenting long strings of heard songs into smaller subsets or packages, by a process reminiscent of the chunking of information as a coding mechanism in short term memory. Here we report three tutoring experiments on nightingales that examined whether such 'chunking' was susceptible to experimental cueing. The experiments tested whether (1) 'temporal phrasing' (silent intersong intervals spaced out at particular positions of a tutored string), or (2) 'stimulus novelty' (groups of novel song-types added to a basic string), or (3) 'pattern similarity' in the phonetic structure of songs (here: sharing of song initials) would induce package boundaries (or chunking) at the manipulated sequential positions. The results revealed cueing effects in experiments (1) and (2) but not in experiment (3). The finding that birds used temporal variables as cues for chunking does not require the assumption that package formation is a cognitive strategy. Rather, it points towards a mechanism of procedural memory operating in the song acquisition of birds.

Approaches to the mechanisms of song memorization and singing provide evidence for a procedural memory

Há evidências crescentes de que, durante a aprendizagem do canto, as aves adquirem não somente "o que cantar" (o repertório comportamental), mas também "como cantar" (o programa do canto), incluindo regras de seqüência do canto. O Rouxinol-comum Luscinia megarhynchos adquire essas informaçäes seriadas dividindo as longas cadeias de cantos ouvidos em segmentos ou pacotes menores através de um processo lembrando o corte ("chunking") de informação como mecanismo codificador na memória de curto prazo. Aqui relatamos três experimentos de aprendizagem pelo rouxinol para ver se tal "chunking" é suscetível de marcação experimental. Os experimentos testaram se (1) a "articulação temporal" (intervalos de silêncio entre cantos repartidos em determinadas posiçäes na série aprendida), ou (2) a "novidade do estímulo" (grupos de novos tipos de canto acrescidos a uma série básica), ou (3) a "similaridade de padrão" na estrutura fonética do canto (aqui o mesmo início dos cantos) induziria os limites dos pacotes (ou seja o "chunking") nas posiçäes seqüenciais definidas experimentalmente. Os resultados mostram efeitos de marcação nos experimentos (1) e (2), mas não no (3). A descoberta de que as aves usam variáveis temporais como marcas para o "chunking" não exige assumir que a formação dos pacotes seja uma estratégia cognitiva. Isto melhor indica que um mecanismo de memória procedural opera na aquisição do canto das aves.

From birdsong to speech: a plea for comparative approaches

Linguagem e fala humanas são realizaçäes únicas. Todavia, têm várias características em comum com outros sistemas de comunicação e, portanto, foram comparadas pelos pesquisadores com o canto das aves e os sinais vocais de primatas não-humanos. Paralelos interessantes concernem em particular o desenvolvimento do canto e da fala. Esses comportamentos dependem da percepção auditiva, de memorização subseqüente e finalmente da produção de imitaçäes vocais. Diversos mecanismos ajudam os indivíduos jovens a enfrentar vários desafios durante o período de desenvolvimento dos sinais. Exceto por diferenças específicas, paralelos impressionantes podem ser encontrados também na maneira como um humano e uma ave particularmente capaz, como o Rouxinol-comum Luscinia megarhynchos, tratam a convivência com um grande número de diferentes padräes sonoros ou cantos. Em conseqüência de tal contato, tanto as crianças humanas, quanto as jovens aves podem adquirir amplos repertórios de sinais verbais ou vocais. Todavia, esses feitos requerem acesso a mecanismos de memorização específicos que são bem adaptados aos objetivos que servem, permitindo, assim, que preencham os papeis típicos de suas espécies. Em referência a esses tópicos, o canto das aves é um modelo biológico excelente para pesquisa sobre memória e também um sistema apropriado para estudo de estratégias evolutivas numa classe muito bem sucedida de organismos.

Acoustic communication in noise: regulation of call characteristics in a New World monkey.

This study on common marmosets Callithrix jacchus is the first to examine noise-dependent mechanisms of vocal plasticity in a New World monkey. Since acoustic communication can be considerably impaired by environmental noise, some animals have evolved adaptations to counteract its masking effects. The studied marmosets increased the sound level of their spontaneous calls in response to increased levels of white noise broadcast to them. Possibly, such noise-dependent adjustment of vocal amplitude serves to maintain a specific signal-to-noise ratio that is favourable for signal production. Concurrently, the adjustment of vocal amplitude can maintain a given active space for communication. In contrast to some bird species, no noise-induced increase in the number of syllables per call series could be found, showing that an increased serial redundancy of vocal signals was not used to communicate under noisy conditions. Finally, we examined a possible noise-dependent prolongation of vocal signals. This approach was guided by the findings of perceptional studies, which suggest an increased detection probability of prolonged signals in noise by temporal summation. Marmosets indeed increased the duration of their call syllables along with increasing background noise levels. This is the first evidence of such mechanism of vocal plasticity in an animal communication system.

Can dolphins heal by ultrasound?

In recent years, dolphin-assisted therapy has become very popular and an increasing number of facilities offer therapy programs with dolphins worldwide. To this date, there are no studies concerning the behavior of dolphins during these therapies. As a result of speculations that the echolocation of dolphins may play an important role for the success of the therapy and the high publicity of this in the media, people pay much more for dolphin-assisted than for other animal-assisted therapy programs. Based on publications in medicine, we will show that ultrasound emitted by dolphins could have an effect on biological tissue under some circumstances; such as sufficient intensity, repeated application over several days or weeks and a certain application duration per session. We recorded 83 sessions at the "Dolphins Plus", a fenced area with ocean water in the Florida Keys. Our observations demonstrate that only one out of five observed dolphins behave significantly differently towards patients compared to other humans and that the duration of the observed close contacts did not meet the requirements for common ultrasound therapies.

Dynamic-acoustic variation causes differences in evaluations of laughter.

Exposure to laughter has striking effects on human listeners and may facilitate positive emotional and behavioural responses. The acoustic signal pattern of laughter vocalisations is particularly suitable to elicit these reactions. However, little is known about factors that lead to differences in reactions of listeners. The acoustic quality of laughter, the social context, and the disposition of the listener are possible variables in differences in evaluation. We conducted experiments using playback techniques in which human laughter elicited in a natural setting was evaluated by listeners (N=90). Listeners evaluated several phrases of laughter produced by different laughing targets. We investigated the role of the characteristics of voice, dynamic-acoustic characteristics, and order of playback sequence on the evaluation of laughter. The dynamic-acoustic characteristics of laughter significantly affected evaluations by listeners, whereas voice and the playback order did not. An acoustic analysis allowed us to identify acoustic parameters that contribute to such differences in evaluation.

The use of vocal signals in the social play of barbary macaques.

Field studies in various species of Macaca (Cercopithecidae) provided evidence for specific visual displays that typically accompany playful interactions. The aim of our study was to examine whether and when playing individuals would use auditory displays, i.e. vocalizations that often occur during social play as well. The study was conducted on a population of semi-free Barbary macaques (Macaca sylvanus) with a special focus on the composition and dynamics of playful wrestling (synonymous term: 'rough-and-tumble play'). Analyses of dyadic encounters between subadult males allowed us to distinguish five types of playful behaviours and three types of vocalizations. The latter were clearly linked to encounters where effects of visual signals were impaired, e.g. during close body contact. During wrestling, vocalizations tended to increase in the beginning of an encounter, whereas the last seconds of wrestling often showed a decline in vocalization rate. Our results allowed us to conclude that these vocalizations may supplement or in many cases even substitute interactional effects of visual signals, e.g. the 'play face.'

Dusk calling in barbary macaques (Macaca sylvanus): Demand for social shelter.

Barbary macaques (Macaca sylvanus) show an increase in vocal activity at dusk. This investigation showed that these vocalizations were mainly produced by juveniles from six to 18 months of age, during their attempts to achieve body contact with their mothers, thereby building up a sleeping cluster. The "dusk calling" consisted of protracted sequences of variable vocal patterns which always ceased when the juvenile joined its preferred sleeping cluster. The length of the sequences corresponded to the time it took the juvenile to be accepted into a sleeping cluster. One-year-old juveniles exhibited the highest vocal activity. The similarity of the results obtained in two outdoor enclosures in France and of those in the field (Morocco) indicated that dusk calling is common to this species, and not a behavior unique to captive animals. © Wiley-Liss, Inc.

Communal roosting and formation of sleeping clusters in barbary macaques (Macaca sylvanus).

Sleeping cluster composition and distribution were studied in a semi-free-ranging population of 174 Barbary macaques (Macaca sylvanus) in Rocamadour/France. Over a period of 2 months 341 sleeping clusters comprising 754 animals were recorded as animals left the sleeping trees. To control for nocturnal activities five observation periods were conducted, each of which covered a complete night. Sleeping partners were selected from a particular set of individuals. From night to night there was considerable fluctuation among the individuals, which finally formed a sleeping cluster. Preferred size of sleeping clusters was two and three individuals per cluster. The majority of females spent the nights in body contact to infants or female juveniles; whereas males either slept alone or with older male juveniles. Adult males and females never shared a sleeping cluster. During the night the animals showed hardly any locomotive and vocal activity. Sleeping clusters remained stable until dissociation the next morning. © 1992 Wiley-Liss, Inc.